Process of smelting ores of volatile metals



Feb. 16 1926.

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:dii/sys more particularly Patented F eb, 16,)1926.l

WILLIAM A. OGG', OF NEWTON, MASSACHUSETTS.

PROCESS or SMELTING omas or votATILF METALS.

Applica/c1011 mea February 7, 1925. sei-iai No. 7,561.

To/ all whom il? may concern/f Be it known that I, lVILiiIAM A.' OGG, a

citizen of the United States, and a' resident of Newton, county ofMiddlesex, State of l\Ia'ssacl1-usetts,have `invented an Improvement inProcesses of Smelting Ores of Vlatile Metals, of which the followingldescription, in connection with the accompanying drawings, 'is aspecification, like characters on the drawings representing like parts.

y My invention relates to the smelting of material bearino'volatilizable metals, particularly but notexclusively natural orconcentrated ores of zinc, and has among its objects the accomplishmentof an increased recovery of the metal values' at low cost by animprovement in thatprocess of smelting practiced with retorts andcondensers. My

improved method, which may be so .prac-4 tjced as to increase theoretreating capacity'- of a`given,f urn ace, securing a higherpercentage recovery of themetal values,an increased yield of spelter"per'retort, and in addition to@L produce 'directly' the zinc bearing/oreproductsA of, high economic value hitherto produced only by"mor\e costlyprocesses involving-'the treatmentof vmetallic zinc, will be bestunderstood. from the following description when read in .light of theaccompanying drawingsV showing one form of Y,apparatus for practicing myinvention, while the scope of my invention will be pointed out intheappended claims. j y In the dravfing:-` l Fig. 1 shows more or lessdiagrammatically anf arrangement of apparatus for prac'- ticing myinventiony-and y Fig. 2 is afsection on the line'Q-QOR Fig. l. Thefurnace commonly used for thereduction of Zinc ores'or ores. of`1ikevo1atil izable 'metals includes tiers of 'cylindrical I retortscommonly made lof fire clay or other suitable refractory material, whichretorts are removably supported in the combustion i' chamber of thefurnace. The ore which may be natural oxides, or sulphides converted toxides by roasting,' is mixed Lwith reduction fuel,usually coal or cokefree as far as pos- .crease 'the coo `above that of the condenser now.commonlyo i, liquefy t sible from sulphur, and the mixture c argedlinto the retort. Injpracticewhen sm l-tin zincbearing ores theretortsare subjected `to a temperature of about 1300 degreescentigragle, which reduces vthei ore, and being above the boiling pointofzic volatilizes the metal which passes out of'the retort in the formof a vapor andi is condensed -to a lip'uid in a condenser, the latterconsisting o `a shortI frustoconical continuation of the -retortprojecting from the combustion chamber and being commonly detachably.connected with the retort,

In practicing the smelting rocess now commonly employed with existingapparatus the re ulation of the .amount of retort charge an temperatureis av matterfof great nicety. The limitations ofthe material used formaking the condensers, initial cost, and handling chargesmake it imractical to ining surface o the condenser employed. The. limitation tothef'use of .a condenser with ya relatively small cooling surfacetherefore makes it necessaryin 'practice to limit the charge yin theretort to a value which willgproduce a rate of Vapor discharge into: thecondensernot in excess of the ca acity of the condenser veiiiciently tolie metal. This charge is materially below vthefull cubical capacity ofthev retort the practice of; the process by the condenser reducethe-output of the furnace, and in addition" make 1t necessary closely toregu- -and consequently the limitationsplaced on late the temperature toreduce to a' minimum y the losses. due .to escaping vapors from themouth of the condenser. With existing apparatus the metallurgistisconfronted with two alternatives, that of running with the condenserstoo' cold with consequent production of a high percentage of blue powderwhich will have to be redistilled with further losses, or thatofrunningwith the condensers too hot with consequent loss of vapor fromthe mouth of the condenser.

By way of an example of goodc practice with the prior. method the retortis loaded with mixed gre and fuel to roughlyf'percent of its cubic'alcapacity. The recoveryv of metal contentis about 89.5p`percen'tin f' ofair the form of spelter, and of the remainder about 7.75 percent is inthe residue, about lpercent is absorbed by the walls of the retort andcondenserkfand the remaining loss of 1.75 percent is principally intheform of escaping vapors from themouth ofl thecondenser whiehvvit isuneconomical to attempt to recover. The4 recovery of 32 pounds pertwenty-four hour day of metal value in the formof spelter may beconsidered the maximum capacity of the condenser in itsV normaloperation with thel prior method.

Because of the increasing.,r prices of coal and labor and increasingoverhead charges necessary to the performance of the prior method theexpense ofproducing the product has increased greatly and one object ofthe present invention is both to permit more ore to be treated atonetime and to increase the percent/recovery of metal values, thusminimizing the expense per unit of commercially available metalproduced. In accordance with the invention the retort is deliberatelysubstantially overcharged beyond 'the capacity of the condenser to con-vdense eiciently, and as a purpose of the invention is to secure a largerecovey of (spelter the condenser is operated at full conensing capacityfor the given operating conditions. Suicient heat is applied to theretorts. substantially to^reduce all the metal which is in oxidized formand a substantial fraction of the metal values -is intentionally caused.to escape from the condenser land is recovered by othermeans.'v By thisdeliberate overcharging of the retort so that a substantial percentageof the metal values vaporizedis passed out from the condenser anincreased recovery of spelter per lretort is obtained, while theremaining metal values as will be pointed out later are collected ashighly valuable products. A

Referring to the drawing I- have shown a furnace 1 of the regenerativetype in which are formed gas passages 3 connected .by means of suitableVflues 5 andjports 7 to combustion chambers 9. In the combustion chambersare arranged tiers jof retorts 11 each of whichJ is provided with acondenser 13 projecting beyond the front of the furnace. The furnacedescribed is of'a common type and per se forms lno part of my invent1on.A. .Y

-In practicing my invention I attach to the front of the fur-naceoposite the condensers suitable hoods 15 Whic -may be supported in anysuitable manner as for example by providing them Awith the flanges 17fitting a channel 19 carriedby the front of the furnace. .Each`hood isprovided with observation holes v21\-vlfhich may be 'provided withdampers 22 for regulating the amounts dmitted. h `hood is connected bjymeans of a pipe 23 having a gate valve 25' to a main suction pipe 27leading to an exhaust fan or blower 29 so that the vapors escaping fromthe condensers maybe conveyed froxm the furnace to suitable collectingmeans for the vapors, and for this purpose I have shown the dischargevpipe 31 of the fan leadingr to cooling chambers 33 discharging into abag house 35 in which are suspended cloth bags `37 releasably closed attheir lower ends by any suitable means 39, as for example a cord. iConveniently the vapors escaping from the condensers.v are burned in thehood to provide zinc oxide, and as the vapors are burned in a relativelycool atmosphere due to the excess of air, the zinc oxide is sud-- denlychilled to roduce a very fine powder easily handled by the conveyingmeans and having in itself a high commercial value.

Preferably the condenser mouths arc plugged with a mixture of screenedanthracite dust with enough ore to give it body which provides a porousplug for the condenser mouths acting as a filter which frees the vaporsfrom dust and other solid impurities and further acts to materiallyprevent the escape of heavy vapors such as the lead content of the ore.

In operation if the ore charged'has an appreciable cadmium content .thesame largely may be `segregated from the bulk of the zinc contentdischarged from the] condensers due to the fact that the cadmium orereduces at -a lower ktemperature and consequently more rapidly than thezinc, which makes it possible first to pass olf vapors rich in cad-4Amiumand then after it has been determined that the most active reductionof cadmium is completed to open the bottom of the bags in the bag houseand shake them to recover a product rich in cadmium, or if desired thishigh cadmium bearing fume may be collected in a separate bag house orsettling chamber. .Isls the lead content of the ore .at ter reduction isless volatile than the zinc practically all the lead is collected in thesov ico

condensers resulting inthe production of zinc roxide low in discoloringlead impurities, and if an ore low 1n cadmmm be pro# vided because ofthe substantlal elimlnatlon lof the lead content and the 'burning of thevapors in a large excess of air the zinc oxide, after a subsequenttreatment if necessary to remove carbon, will be analogous or equal inquality to thezinc oxide produced by the so called Fre lch processconsisting of burning metallieziinc.

It will be noted that my improved process A avoids the previouslymentioned alternative of running the condenser so cool compared to therate of vapor How fromthe retortsas to produce la substantial portion ofthe metalvalues `as blue powder, and that as a consequence it-is notnecessary to use` the same degree of care in lcarrying out my same timeIthe current of air induced by Jthe exhaust fan is directed over theconden'sers which it is believed keeps them cool enough as compared tothe increased rate of vapor flow to function tocondense an increasedamount ofspeltcrper retort'as compared with the prior process. As anexample of my yimproved method without limitation thereto I have found'that M a retort furnace having 405 retorts, using v280 retorts forroasted oreand 125 rctorts 3() pounds of reduction fuel consisting of.

, approximately 5 pounds of anthracite coal f and pounds of coke breeze,the nine content' of the roasted ore averaging 69,4 pounds per retort.If Athe return products resulting from the smelting operation given asan example are assumed to be equal in metal value to the return productscharged from the next preceding operation, which assumption I have foundtoy be approximated in practice, then @the total production of metalvalues represents the recovery from the ore charged, which means thatthe spelter recovery` averaged 57.7 pounds for each. retort/charged withore. This spelter -recovery represents 83.1 percent of the metal valuescharged in the form of ore, and at the' same time there was recovered inthe bag house a productrepresenting 3.1 pounds `of zinc per retort ofthe total 405, retorts or 4.5 pounds per retort charged with ore, rep

resenting 6.5 percent of the metal' values of the .ore charged. Thetotal recovery of not'returned tothe furnace. a

As an example of the' prior method I have -found on the same basis ofcomputation lnrthe example given above, thatawith the same retortsv andfurnace. a retort' charged with/'7 pounds of roasted ore of the samecomposition having a metal content of 52.2y

pounds mixed `with 28v pounds of the same kind of reduction fuelproduced 46.7 pounds of spelter, the latter`represent'i"ng 89.` per centofithe metal values of the ore charged.

'fhus it will be noted that-not`only does my imp rovedprocessO increasethe furnace output but it also secures an increased recovery.v

of the metal values with' a smaller ratio of reduction fuel totheroasted ore charged,

`all of whichwill be'iapp'arentfrom an inspection of the following tablesummarizing` the results of the above examples of my in- ,proved methodand thel prior method.

Improved Prior method. method.

Number of retorts charged with ore. i 280 280 Number of retortschargedwith return prodi ucts 125 125 Ore charged per retort chargedwith ore 98. 2# f 75# Fuel charge per retort charged with ore 30# 28#etai value of ore per retort charged with ore. 69. 4# 52. 2# Spelterrecovery from ore per retort charged.l

with ore 57.7# 46. 7# Percent metal recovery from ore in bag house 6. 5None Total percent recovery of metal values of ore charged 92 89. 5

i In the above example of my improved erage atotal :volumetric capacityof 1.41 cubic Dfeet, and the charge per cubic foot of charging theretorts with tore` and reductionV fuel to theirfull cubical capacity, inwhich vcase the output of fume and spclter will be correspondinglyincreased 4without it being4 necessary materially to increase. thereduction temperature. Conveniently this may be ldone by briquetting theore and fuel, in which case a'mixture of ore and reduction fuel mixedwith a suitable binder will .be formed into briquettes under pressure,thus increasing the amount of metal values that may be charged Linto aretort of given cathis total retort capacity amounted to 69.7

pacity. As As'uitablefor this purpose I may use a mixtureof 70 cokebreeze,fand 5 ercent of pitch, which ercent of roasted ore, 5 percent ofanthracite coal, 2O percent of mixture can be briquetted in'any suitablebriquette making machine.

The amount of zinc oxide` produced by my' method can be varied byvarying either the charge or temperature or both, but preferably byvarying the charge. In the above example of hny method the temperaturewas raised gradually fromA about 1000 degrees centri` grade, at whichtemperature. the reduction prccess will begin, to a maximum of 1450degrees centigrade, reaching the` latter teinperature after theoperation had continued for about 14 hours, and was maintained at thatImaximum temperature for about 5 hours, or until jhe operation wascompleted.

By reducing this maximum temperature pr' furnace, but theproposedprocess has been y escaping from the condenser, which losses arenecessarily low as heretofore explained, and the proposed'process is notpract-ical as the cost would be greater than the returns. \Vith myimproved method, on the contrary, I. p'ropose deliberately to overchargethe retorts as compared to the condenser capacity and to collect aneconomically material proportion of the metal charged to the retortafter it has passed through the condenser as a sublstantial andintentional factor in the process. At the same time spelter recovery isan important object and -the con-` densers are operated under suchconditions as will secure a maximum production of that product. f

l/Vhile the process as described has some aspects of fractionaldistillation, especially in the selective recovery of lead and cadmiumif present, itcis primarily a smelting process of treating ore or othercrude zinc bearing material With reduction fuel.

An import-ant feature of the invention is the possibility of productionin substantial quantity of a high grade. zinc oxide although in a senseas a by-product of spelter production, and it Will be observed thatin'absence of a market for thezinc oxide the same may be charged to theretorts as a concentrated product rich in zinc.

The invention is applicable to existing installations of retort furnacesand is exceedingly simple, requiring only amoderate installation chargelfor alteration of the usual existing plant arranged for carrying outthe prior method of 'spelter recovery. As a larger amount of ore may betreated in each retort at one time, an economy of expensive heating fuelper` amount of ore treated is realizedfor it Will-be observed thatfurnace heat losses are substantially independent of, the amount of orecharged. v.Also .as a greater amount of ore is heated at one time theoverhead and labor charges ire correspondingly reduced. The maximumeffective production of metallic spelter is provided for, yet aconsiderable'fraetion of the metal values is lrecovered exterior-ly ofthe condenser. .y

Although I have. described for purposes of illustration one specificmanner of carrying out my improved method it is to be understood that Iam notlimited thereby to its particular details as deseribed,but thatWithin the scope'of my invention wide deviations may b'e made therefromWithout departing from the spirit of my` invention.

1 That method of smelting crude zinc bearing material utilizing aretortfurnace and condenser, which consists' in charging the retort 'with )amixture of said material and reduction fuel in amount to produce andcondenser, which consists in charging the retort with a mixture of saidmaterialv and reduction fuel in amount to produce .a volume of metalvapors in substantial excess of the capacity of the condenser fully tocondense .the same and ,conducting the vapors discharged from thecondenser, which .comprise a considerable fraction of the metal valuesin the material treated by a current of air, for recovery by deposit ofthe metal values therein while obtaining a recovery of spelter in the'condenser to the full capacity thereof.

3. That method of smelting crude zinc bearing material utiliz-ing aretort l. furnace and condenser, which consists in charging the retortwith a mixture of said material and reduction fuel in amount to producea volume of metal lvapors in substantial ex` cess of the capacity of thecondenser fully to' condense jthe same and conducting the vaporsdischarged from the condenser, which comprise a considerable fraction ofthe metal `values in the material treated by a current of air directedagainst the condenser, for

recovery by deposit of the metal values therein while obtaining arecovery of spelter in the condenser to the full capacity thereof. LLThat-.method oi smelting crude zinc bearing material utilizing a retortfurnace and condenser, which consists fin .charging the retort with amixture of said material and reduction fuel in amount to produce avolume' of metal vapors in substantial excess of the capacity of thecondenser fully Y to condense the same and burning in an excess of airthe vapors discharged from the condenser, which vapors comprise a.considerable fraction of the metal values inthe materialv treated, toproduceatinely divided oxide While obtaining a recovery of spelter inthe condenser to the full capacity thereof.

5. That method of smelting crude zine bearing material utilizing aretort ,furnace and con-denscr, which consists iii/charging the retortwith' a mixture of sai/d materiali and reduction fuel-` in amount tproduce a volume of metal vapors 1n sul stantial excess l.of thecapacity of the condenser fully to condense the same and burning inanexcess of air the vapors discharged from the condenser, which vaporscomprisel a con.- siderable fraction of themetal values in the masciamaterial treated, to produce a finely divided least 2.5 percent of thevmetal vvalues to be 05 oxide While obtaining a recovery of spelter inthe condenser to the full capacity thereof discharged yin the form ofvapor from the condenser mouth, directing a current of air andconducting the oxide by a current `of air against the condenser toIincrease its spelter for recovery therefrom by deposit.

6. That method of smelting crude zinc bearing material utilizing aretort furnace and condenser, which .Dconsists in charging the retortwith a mixture of said material and reduction fuel in lamount vtoproduce a volume of metal vapors. in substantial excess of the capacityof the condenser fully to condense the same, directing a current of airagainst the condenser to Vincrease the spelter-produ'cing capacitythereof, burning in said current of air nthe' vapors discharged from thecondenser, which comprise a considerable fraction of the metal values inthe material treated to'produce a finely divided oxide and conductm'gthe oxide by saidn current of air for recovery therefrom by de osit.Thatmethod of smelting zinc bearing material utilizing a retortv furnaceand condenser, which consists in charging the retort with a mixture ofsaid material and reduction fuel in subst-antial excess of the capacity.of the condenser to condense fully the resulting metal vapors, burningthe vapors discharged from the condenser in a current of air to producea finely divided oxide, and collecting the oxide from said air bydeposit in successive fractions to recover a fraction high in cadmiumand a `second fraction lower in cadmium While recovering spelter in thecondenser to the full capacity thereof.

with condensation therein of substantially all the lead content of thematerial. l

8. That method of smelting zinc b aring material utilizing a retortfurnace an condenser, which consists in charging the retort with amixture ofnsaid material and reduction fuel suficient lin amount tocause at least 2.5 percent `of the metal values' to be .discharged in)the form of vapor from the condenser moutii, and entraining said vaporby an air current flowing past the condenser mouth for vrecovery fromsaid air by deposit.' 9. That method of smelting zinc bearing materialutilizing a retort furnace and condenser, Which consists in chargingtheretort with a mixture of said material and reduc tion fuel sufficient in.amount to cause at least 2.5 percent of the metal values to bedischarged in the form of vapor` from the condenser mouth, burning saidvapor to proddee an oxide, and entraining said oxide a current ofy airfor recovery from said air by deposit. s

.10. That method of smelting zinc\bearing material utilizing a retortfurnace and condenser, Which consists in charging the retort with amixture of said material and reduction fuel ,sufficient in amount tocause at material utilizing a retort furnace and conl denser,Which'consists in charging the retort -to substantially its fulllcubical capacity With a mixture of said material and reduction fuelsuiiicient effectively to reduce the metal values'and 'to produce Aavolume of metal vapors inl substantial excess of the capacity of thecondenser fully to condense the same, burninginfair the vaporsdischarged from the condenser mouth, which comprise a considerablevfraction of the metal values in the material treated, entraining theresulting oxides in a current of air, and recovering the oxides fromsaid current of air by deposit.

l2. That method of smelting zinc bearing material utilizing a retortfurnace and condenser, which consists in charging the retort tosubstantially its fullcubical capacit'y with a mixture of said materialandl reduction fuel sufficient effectively to reduce the metalvaluesand'to produce a volume oft'metal vapors in substantial excess ofthe capacity of the condenser fully to condense the same, directing acurrent ofair against the condenser to increase the spelter producingcapacity of said condenser, burning the vapors discharged from thecondenser mouth in a current 'ofl a1r, and recovering the resultingoxides from said air by deposit.

,' 13. That method of smelting zinc bearing material utilizing -a retortfurnace and condenser, Which consists in charging the retort `With amixture of said material and reduction fuel in substantial excess of thecapacity of the condenser to condense fully the reslting metal vapors,converting the vapors' discharged from the condenser pound in a currentof air, and separating the compound from said air by deposit.

. 14. yflhat method of smelting zinc bearing material utilizing a retortfurnace/- and com denser, vhich consists in charging the retort with amixture of "said material and reduction fuel insubstantial excess of thecapacity of the'condenser to condense fully the resulting metal` vapors,converting the vapors discharged from (the condenser mouth and whichlcomprise a considerable kfraction of the metal values treated to apulverulent solid compound by treating them with a gaseous substanceWhich Will '.retort to substantially its full cubical capacity with amixture consisting of reduction fuel and a relatively large proportionof said material, heating the. retortby progressively raising the Atemperature to a maximiun, maintaining said temperature at substantiallysaid maximum until the yreduction is vsubstantially completed to produceduring the reduction step a volume of fmetal vapors in substantialexcess. of the capacity of the condenser fully to condense the same,burning in an excess vapors discharged from the condensers, comprising aconsiderable fraction of the `metal values treated, and recovering themetal values from the air by deposit.

16. That method -of smelting zinc bear.

ing material: utilizing a retort furnace and condenser, whichcuonsistsi` in charging the retort to substantially Iits full cubicalcapacity with a mixture of said material and reduction fuel, heatingthe. retort by pro` gressivelyJ raising thetemperature to` a maximum,.maintaining said temperature at substantially said maximum until thereduc'- tion isA substantially completed to produce during the reductionstep a Volume of metal vapors in substantial excess of the capacity ofthe condenser Ffully to condense th same, burning in an'excess of airthe vapors discharged from theconden'sers, ,comprising a considerablefraction of the metal values treated, and recovering the metal valuesfrom'the air by deposit.

17. That method of smelting inc bearing material utilizing a retortfurnace and condenser, Which consists in charging the -retort tosubstantially its full cubical capacity with a` mixture of saidmateriahand reduction fuel, heating the retort by slovifly raising thetemperature to a maximum, maintaining said temperature at substantiallysaid maximum Yuntil the reduction ismsubstantially'completed to producedurif"iz"the reduction step a volume of metal Avapors in substantialexcess of the capacity of the condenser fully to condense the same,burnl ing 1n an excess of air the vapors discharged from the condensers,comprising a con--` Siderable --fraction of the metal values treated,land recovering 'the metal values froml the airby deposit.

y 18. That method of smelting zinc bearing denser, which consists incompressin material utilizing a retort furnace and condenser, Whichconsists inchargin'g the retort to substantially its full cubicalcapacity with a.mixture of reduction fuel and said 'material, heatingthe retort by starting at substantially .the temperature at whichreduction will begin, progressivelyraising this temperature to a maximummaterially in excess of thev starting temperature and maintaining saidtemperature at substan-A from the condenser mouths, comprising a"considerable ,fraction of the metal values' treated, and recovering themetal values from said air`by deposit. 19. That method of smelting zincbearing material utilizing a retort furnace and con-d of air the denser,Which consists 1n compressingl1 a mixture of said material and reductionl, charging the retort With the compressed mixture in amount-to producearate of vapor flow in excess of the. capacity of the condenserefiiciently to condense said vapor, burning in an excessof air the.vapordischargedy from the condenser mouth, comprising a considerablefraction of the metal values treated, and drecovering the metal valuesfrom said'air by deposit. l

20. That method of smelting zinc bearing materiahutilizing a retortfurnace and cona mixture `of said material and reduction nel, chargingthe retort with the compressed mixture to substantially the full cubicalcapacity of said retort to produce a rate -of flow of metal vapoiry insubstantial excess of the' capacity of the condenser fully toI condensethe same, burning in an excess of air the vapor discharged from thecondensery mouth, comprising a considerable fraction of the metal valuestreated, and recovering the metal values from said air by deposit. d

21.- That method of smelting zinc bearing material utilizing a retortfurnace and condenser, Which consists in briquettingA a mixture of saidmaterial and reduction fuel,

charging the retorts With the briquettes in amount to produce a rate ofvapor flow in substantialgggexcess of` the capacity of the condenserefficiently to `condense said' vapor, burning in an excess` of air thevapor discharged from the condenser mouth comprising a considerablefraction of the metal values treated, and recovering the metal valuesfrom said airl by deposit.

22. That method of smelting zinc bearing material utilizing a retortfurnace and con-l denser, which consists 1n brlquettlng a mlxture -ofsaid material and reduction fuel, vapor"dischargefrom the condensergzouth, charging the retorts with the vbriquettesto comprsing'aconsiderable fraction bf the substantially the full cubieal capacity ofmetal ,values treated, and recovering the l0.

saidretort to producel a rate o flow ofmetal values from said air bdeposit.

5 metalA vapor in substantial excess of the `In testimony whereof, I avesigned my capa ty of the condenserfully Ato condense name to thisspecification. v the same, burning in an excess ofv airthe A

